(Apologies for the long post)
Apart from putting finish on guitars, the binding process has been my biggest frustration. My guitars have big arches on the top and backs, both laterally and longitudinally and cutting channels around the upper/lower bouts and waist areas has been very frustrating involving lots of cuts altering both depth and width.
I use a Makita laminate trimmer, which is light enough hand held and comes with a side following attachment that lets me use ordinary router bits rather than those with guide bearings. This has the power, but the base area is too big to follow just the edge (hence the bout/waist problems). The solution is to put a raised area on the base close to the cutting edge of the bit with a very small surface area to follow just the edge. This, however, makes the trimmer very unstable hand held.
Having done some research, Don Williams' jig was the perfect solution to give me stability. I want to have the trimmer moving round the guitar as I think this gives me better control in areas such as the bottom and top of the guitar where purflings have to be mitred. I set myself the goal of producing the binding and purfling ledge in width and depth with just one pass of the cutter.
Getting to the end of making Don's Jig (thanks for the great info on your website Don!!) I realised that I would not have freedom of motion in all of the directions I required. Don's jig can only adjust the angle the trimmer meets the guitar via the movement from the main Lazy Suzy bearing, so if you are, say, going round the lower bout into the waist area then the trimmer stays more or less at the same tangential angle to the perpendicular sides. The round donut on the base means this keeps the trimmer on the top but it bridges longish lengths in places. With the more common arching used on guitars this wouldn't be a problem, but with the degree of arching I have on my guitars the bridging of the donut would not give me a uniform depth binding channel in these critical areas. Hence I needed the trimmer to swivel, to keep the small "follower" on the top/back edge and the routing bit and guide perpendicular to the sides at all times.
I have had to do a modification to Don's design to enable this that you may be interested in - apologies if it has been done before and I have not seen it. I have achieved this by putting another smaller Lazy Suzan bearing in the part of the jig that holds the trimmer. The follower is a small rubber tap washer (real kitchen sink solution this!!). The beauty of it for me is that I can use just the one router bit to cut the binding/purfling channels and adjust the depth and width of cut on the trimmer. I have set it up for a 11mm double flute (I have found this wide enough for all of the binding/purfling combinations I use) and this drops through a 13mm hole drilled in the new base plate.
Here are some pictures:
First an overview:
Then the business end of the jig on the guitar:
More detail from below. You can see the Lazy Susan Bearing and the small rubber tap washer sitting on the edge of the top as the bit cuts:
And finally a shot from below of the plate attaching to the trimmer base and the tap washer:
I did the first "route in anger" yesterday and although I didn't quite meet my target of one cut/pass it was pretty darned close. The area around the lower edges of the lower bout need a second pass with a slightly bigger width of cut, but the jig keeps things so stable that this is not too hard. When I had to do this by hand it was a nightmare. I think the follower could move even closer to the edge of the router bit - maybe even have it with a hollow core that the bit comes through. This would have the top/back pivot point immidiately behind the cutting edge, but the amount of area on the top/back would be very small and there would be a risk of the trimmer dropping off the top. Probably best to leave it as is and do a second trimming cut.
I'll be putting a page on my website with more details of the construction soon if people are interested.
